each room in hotel has one switch(buzzer) which is connected to the main panel of LED placed on the reception ..so that the receptionist can know which room needs a room service. . .
this is exactly wat i need. .
but instead of rooms in my project its "flats". . .
the main panel of LED would b placed at the gatekeeper room.so whichever flat will turn its switch on,the corresponding led of the flat in the panel will glow.
so pls suggest how to go for the wirings. . .
there are 120 flats in the society..
please help????

 

Split each floor of the flats into a manageable block of units.

Use single pair of wires looping to each block of units (i.e. 12 units). Each switch is normally closed and has a resistor across its terminals.

Flat 1 has a 500R resistor, Flat 2 has a 1k resistor, Flat 3 has a 2k resistor, Flat 4 has a 4k resistor, Flat 5 has a 8k resistor.

Measure the resistance or use an A2D port on a PIC microcontroller.

If 8.5k is measured you know Flat 5 and Flat 1 have pressed their buttons
If 3k is measured then flat 3 and flat 2 have pressed their buttons
If 15.5k is measured then all flats have pressed their buttons and there is probably a fire somewhere.

 

What's the difference between a 'flat' and an apartment?

Anyway, isn't there some resistance with a long run of wire? At the time in my education, I thought it trivial... but think its several ohms per hundred feet (or was that meters). Anyway, with the wire run and component tolerance, quite a job calibrating for 120 units.

Personally, I'd go with a phone line and an answering machine. Don't need someone to monitor the LED panel, and you get some description of why you are being summoned, and can deal with high priority problems first.

 

However quite simple when calibrating for 12 units as suggested.

The wire resistance is almost constant and can be subtracted out.

I've used a variation on this method. It works.

 

A PIC is overkill for this simple circuit!

Hint: Flip Flop Switch, Dual Inverter Switch

__________________
MechTronics

World of Warcraft is a disease

 

I think a lot of the point of using the PIC is that you have one to service each set of 12 or so flats (apartments), and then that way you cut down on the amount of wiring to the main panel. Who would want to lay all that wire, one pair from each flat to the panel? How much would it cost? Where would you put it all? Ow! Conversely, PICs are very cheap (at least here) and small.

So if instead you can have one pair from each group of flats to the panel, then you've reduced the wiring by quite a lot. Now sure you could do the same sort of arrangement in each group by using a few discrete components instead, but then how easily can you transmit the data of who in that block pressed their button, to the main panel? With a PIC you can convert this into serial data to go to the panel. Hell, you could even have just one pair of wires connect to the panel and attach the PICs to it in a bus configuration, although that's getting to somewhat more complex programming.

It does have a conspicuous problem though, yes: he'd have to be able to obtain and program PICs Needs suitable hardware, and also the ability to write software (or to get someone else to). If that's no problem, then it'd also want a fair bit of testing before being installed.

You do also need a little extra electronics in the main panel to decode all this serial data, and note that one PIC alone wouldn't be able to handle 120 LEDs directly...

 

thnk u very much for ur suggestions
i really appreciate it. . ..
as i am nopt very good with PIC.so wat i hav in my mind is that conenct a group of 16 flats to a single multiplexer and then decode the signal using a D-MUX at the control panel . . .the problem in this circuit is that wat will happen if two flats simultaneously turns there switch on. .

 

wat will happen if 2 flats will turn there switch ON at the same point of time. .

 

Because of the way the resistors are specced you should always be able to tell which flat(s) have pressed the button - even if they all press their buttons you can still work it out via the resistance.

For example on the above - with no buttons pressed (i.e. all closed) then you will have 0 ohms (actually you will have the nominal resistance of the wire).

If all switches are on (open) then you'll have 500+1000+2000+4000+8000 = 15500 ohms resistance across the loop. If flat 5 turns theirs off then its 15500-8000 ohms = 7500 ohms

Have a play with the maths and you will see what I mean.

 

if two flats total is equal to one flats resistance then wat will happen . .
like
flat1=1000
flat2=2000
flat3=4000
flat4=5000
flat5=6000

if flat2 and flat3 will turn on then it will give 6000 ohms
then there will be an ambiguity that might b flat 6 has turned on.
isn't it?

i

 

You need to look more carefully at the set of resistor values that picbits specified. They are carefully chosen (each resistor is twice the previous one) so that there are no ambiguities.

 

It seems to me that cabling-up all those rooms just to have a very basic signaling system may be not cost effective in the long term.

Why not just install a data network and also provide an IP phone in each room.

Perhaps you could then recover some of the installation costs by charging the residents for internet and phone service.

 

I'm glad you posted that - I spotted this message just as I logged off last night and had that horrible feeling I might have got my values wrong

 

i got it . . its really a good idea . .but as i mentioned that i not good in microcontroller. .and i am new to the feild. .so some one told me to go for mux and i did quite study on the subject . .wat i hav now withme is this circuit
http://www.mediafire.com/imageview.p...yz3dh0&thumb=4
making group of 16 flats using single mux for eah grp. .
but the problem now is that wat happen when 2 flats simultaneously turn the switch on. .
pls help

 

That circuit is great if only one person turns on their switch but as you say - what if 2 or more do.

Other than getting rather complex with the multiplexing and reading the values in with a microcontroller my idea with the resistors would be far easier.

For someone who has experience in PIC programming its only about a days worth of work to knock up a working prototype and sort out the programming.